DE2812395A1 - MAGNETIC BRUSH DEVELOPMENT DEVICE FOR AN ELECTROPHOTOGRAPHIC COPY DEVICE - Google Patents

Description

The invention relates to a magnetic brush developing device for a powdered dye image transfer type electrophotographic copier having a fixed Cylinder, which is a photosensitive moving with respect to it Element faces and encloses a rotatable magnetic element, a reservoir and a Having means for dispensing magnetic dye particles onto the cylinder. The term chosen here "magnetic Dye particles "is not necessarily intended to mean that the particles themselves are magnetic but that they are magnetically attracted.

Extensive research has been made recently on development facilities which are based on the one-component developer development method work, because with a sol-

809839/0939

Chen one-component dye changes in the mix ratio of the dye particles and the carrier material such as cannot occur with the two-component developer, which simplifies the maintenance of the copier result.

While the development process described above with one-component developer for direct copying machines, such as those of the so-called electrofax type is very effective, there are various problems with it when it to be applied to dye image transfer type copiers. In particular, in copiers of the powder dye image transfer type, when developing and transferring with the low resistance magnetic dye which is to be used for direct copying devices, smears or obscurations, i.e., indistinct contours in transfer, although developing is carried out favorably at high density. Such a described disadvantage can possibly be attributed to the fact that because of the low V / resistance The dye particle charges that make up a transfer material or has copy paper to which dye particles are transferred when the dye particles are transferred to the copy paper, so that the copy paper and the dye particles have the same polarity, from which it follows that the once on the Copy paper transferred dye particles from this copier

809S3i] / 0939

paper or repelled by the surroundings of the part of the copy paper that has become the image. Therefore should be such a one-component developer used in dye powder image transfer type copying machines should have a high resistance. However, dye particles that can be magnetically attracted and that for convenience, referred to as magnetic dye particles, for conventional magnetic brush development equipment is used, there is a disadvantage that the density of copied images is mostly low because in such magnetic brush developing devices, the magnetic force acting on the dye particles is proportionate is great.

In order to avoid the disadvantage described, is customary Manner, for example, in Japanese Laid-Open Patent Application 51-10534-5, 'proposed a developing device in which the development time has been made relatively long in order to obtain high-density copied imagesj however, such a copier has the disadvantage that undesirable parts of the copy which are not part of the image are produced Fogging occurs, which deteriorates the quality of the copied images.

It is therefore an important object of the invention to provide a magnetic brush developing device for an electrophoto-

$ 09833/0939

Dye powder image transfer type graphic copier to create, in which magnetic (magnetically attractable) dye particles are used, with the better copies with high density without fogging in the parts of the copy that are not part of the image, im the disadvantages of conventional copiers of this type are essentially avoided.

Another important object of the invention is to provide a magnetic brush developing device of the above which is simple in structure and accurate in operation and incorporated in the copying machines of this type at a low cost v / can earth.

The solution according to the invention is that one in the working direction Additional developing device arranged in front of the point of closest approach between photosensitive element and cylinder is provided, which has a arranged on the cylinder development electrode, the photosensitive Element shows and is approximately the same distance from it everywhere, and that one for removing excess dye particles by the photosensitive element determined area or a device is provided, the or between Cylinder and photosensitive element is arranged in the working direction behind the additional developing device.

6098 5.9 / 0939

• copy

The magnetic brush developing device for a powder dye image transfer type electrophotographic copier of the present invention contains an outer cylinder which is arranged to hold a photosensitive element or photoreceptor opposed, a magnet roller which is rotatably housed in the outer cylinder to be rotated to become a dye tank or container containing magnetic (magnetically attractable) dye particles and in the Near the outer cylinder is arranged to hold the dye particles on the outer cylinder, an additional development area for developing with sufficient density of what has become an image Part of an electrostatic latent image formed on the photosensitive member and a dye removing area for removing at least the dye particles attached to the parts of the electrostatic latent image cling to that have not become an image. The additional development area is arranged in the working direction in front of the position at which the surface of the outer cylinder is closest to the surface of the photosensitive member; in this additional development area a developing electrode is provided on the outer cylinder facing the surface of the photosensitive Element shows and has approximately the same distance from the photosensitive element everywhere, while the dye-removing element Area in the working direction behind the additional development area and between the outer cylinder and the photosensitive Element for removing the dye particles is arranged,

609839/0939

- 5 - COPY

/ lir

which adhere magnetically and / or electrically to parts of the copy that do not form part of the image. In particular, the above-described arrangement according to the invention are observed, although the dye particles that pass through the parts of the surface of the photo-sensitive element are attracted to the latent Are connected to the charge of the latent image by strong Coulomb forces that dye particles, which are attracted to the parts that have not become an image and are responsible for the undesirable obscurations are held there only by extremely weak Coulomb forces or only by mechanical forces and are light can be removed by externally applying a bias voltage with a polarity which lowers the degree of development. When using dye particles of high resistance, what will be described later in more detail, the parts that have become the picture only become quite strongly additional developed, with the adherence of some dye particles is initially neglected in the parts that have not become an image, and then these are neglected in the parts that have not become an image Divide adhering dye particles that give rise to The unwanted fogging in copies can be removed to make better quality, high density copies with no fogging on the parts that have not become an image.

The invention is described below, for example, on the basis of advantageous embodiments with reference to the accompanying

609839/0939

attached drawings. Show it:

1 shows a schematic partial view in cross section of a conventional magnetic brush development device to the principle of the development process with the one-component developer to explain;

2 shows a schematic cross section through a preferred embodiment of the magnetic brush development device according to the invention;

FIG. 3 shows a modified view similar to that in FIG Embodiment;

FIG. 4 shows a further embodiment in a view similar to that in FIG ;

FIG. 5 shows yet another view similar to that in FIG. 2 Embodiment; and

FIG. 6 shows yet another embodiment in a view similar to that in FIG.

In the drawings, the same parts are given the same reference numerals Mistake.

609839/0939

281239S

Referring to Fig. 1, the principle of the development method using the one-component developer will be shown. The conventional magnetic brush developing device includes an outer cylinder or sleeve C made of electrically conductive material which is positioned near and faces a photosensitive member or photoreceptor B on which an electrostatic latent image has been formed in a known manner . In addition, the magnetic brush developing device has a permanent magnet or a magnet roller M composed of a plurality of magnets arranged one after the other with alternating polarity. The magnet roller is rotatably disposed in the outer cylinder C to be rotated in the direction of the arrow m. Magnetic, ie more precisely magnetically attractable, dye particles T, which are electrically conductive, form bristles of magnetic brushes on the outer cylinder C when the magnetic roller M rotates counterclockwise, due to the magnetic forces of the magnetic roller M, and move clockwise along the Surface of the outer cylinder C in the direction shown by the arrows t. When the tip of a bristle of the magnetic brush of the dye particles T thus formed approaches the part of the formed latent image with negative charge Q) on the photoreceptor B as shown in (a), a charge of opposite polarity (+) becomes on the outer cylinder C induced. When the tip of the bristle of the magnetic brush continues to move so that it comes into contact with the latent image

809839/0939

which part of the photoreceptor B comes as shown at (b), the charge on the outer cylinder C moves due to the higher electric field strength quickly through the chain of dye particles T through to the foremost of these Dye particles arrive, which then creates a static electrical Force is generated which cooperates with the charge of the latent image, and therefore the charge of the foremost disappears Dye particle when it is combined with the charge of the latent image as shown in (c). Since the magnetic binding force from the magnetic roller M acts continuously on the dye particles T, leaving when the electrical The force of the electrostatic latent image is greater than the magnetic binding force, the dye particles T their chain, as shown at (d) and (e), and are attracted to the surface of the photoreceptor B to form the latent image in to transform a visible dye powder image. At the same time, the parts of the photoreceptor B that do not become the latent image and in which the latent image has not been formed, in which even a small electrical force prevails, the magnetic binding force of the magnet roller M is greater than the electric force, and the dye particles T continue to be attracted to the magnet M without developing the parts which have not become the latent image are.

It should be noted here that the high resistance magnetic dye used in the invention is composed of

809839/0939

electrically conductive and magnetic dyes selected ■ which can be used for development according to the principle of the development method described above is, and that this dye has a relatively high resistance, so that it is suitable for transmission even with the known ordinary corona transfer can be used.

An additional or excess development can accordingly be effected either by the magnetic binding force is reduced or by applying a bias voltage to increase the Coulomb force. On the other hand, can be used to remove the dye particles which adhere to the parts that have not become the latent image and give rise to the undesired ones Giving veils, increasing the magnetic binding force or imposing the bias in such a way that the Coulomb force is reduced. It should be noted here that in order to effect the additional development or to remove the Dye particles responsible for the veil in the non-latent Image parts are responsible like a number of the countermeasures described above in various ways can be combined in the embodiments of the invention which are described below.

Reference is now made to FIGS. 2-6. In Fig. 2 is a preferred embodiment of the magnetic brush developing device of the present invention D1 shown. The development

609839/0939

- 10 -

Device D1 generally includes a fixed outer cylinder or sleeve 3> that or those in the vicinity of and at a distance from a known photosensitive surface 15a or photoreceptor surface of a photoreceptor drum 15 is arranged, which is counterclockwise in a direction indicated by the arrow, a permanent magnet element or a magnet roller 2, the or the is formed by a plurality of magnets, e.g. eight magnets in this embodiment, which have alternating polarity are arranged and rotatably housed in the outer cylinder 3 so that they are counterclockwise in the through can rotate the direction indicated by the arrow, a developing electrode 4 and a dye removing electrode 5 for removal of dye particles, which are not to the latent Picture-taken parts adhere and are responsible for the unwanted haze, and a dye tank or container 13 a, the magnetic high resistance dye particles and is disposed above the outer cylinder 3 to deliver the dye particles T onto the cylinder 3.

The developing electrode 4 has a shape generally conforming to the photoreceptor surface 15a on the drum 15, to form an area for additional or excessive developing, and is in the space between the outer Cylinder 3 and the photoreceptor surface 15a fixed at a position where the on the photoreceptor surface 15a

609639/0939

- 11 -

electrostatic latent image formed is brought close to the outer cylinder 3 while the photoreceptor drum is 15 turns. The lower end of the developing electrode 4 touches the surface of the outer cylinder 3 »while the upper end thereof on the outer cylinder 3 via a mounting plate 11 is attached so that it is spaced from the surface of the cylinder 3. Also is the dye removing electrode 5, which defines an area for removing the dye particles responsible for the unwanted fog are responsible for the parts that have not been formed, arranged in the working direction behind the development electrode 4, i.e. a point in the direction of movement of the dye particles T behind the developing electrode 4 where the Surface of the outer cylinder 3 of the photoreceptor surface 15a the closest. A bias source 8 is with the Development electrode 4 connected to enhance the additional development process while the dye is being removed Electrode 5 is connected to another bias voltage source 9 to reduce the degree of development. The bias sources 8 and 9 are connected in such a manner that when the electrostatic formed on the photoreceptor surface 15a The latent image is negative, the developing electrode 4 is positive and the dye removing electrode 5 is positive negative for the back surface of the photoreceptor surface 15a is loaded. The potentials of the bias sources 8 and 9 are chosen so that taking into account the

009839/0939

- 12 -

Compensating the magnetic binding force with Coulomb forces developed images of sufficiently high density are obtained on the latent image portions of the photoreceptor surface 15a are, not taking into account that to a certain extent responsible for the fog dye particles T on the Parts which have not become the latent image adhere while the potentials on the dye removing electrode 5 are thus set are that they are sufficient to remove the dye particles T attracted to the non-image parts are.

On the other hand, the dye container 13 is> the one above the outer cylinder 3 is attached, with a supply opening 14 provided, which is located in its lower portion and through which the magnetic dye particles T with high electrical resistance contained in the container 13 are distributed over the outer cylinder 3. While the magnet roller 2 is counterclockwise in the stationary outer cylinder 3 rotates, the dye particles T applied to this V / ice are distributed in bristles of magnetic brushes, which extend over the outer cylinder 3 clockwise one after the other over the mounting plate 11, the developing electrode 4, the dye removing electrode 5 and along the Surface of the outer cylinder 3 to move the electrostatic latent image that is on the photoreceptor surface 15a is formed to develop into the visible dye powder image.

809839/0939

. - 13 -

Needless to say, the dye removing electrode 5 applied thereto in the above embodiment has been described, can be omitted if the outer electric cylinder 3 is arranged so that it serves a purpose as in the modification described below.

In Fig. 3, a modification of the developing device D1 of Fig. 2 is shown. At the development facility D2 from FIG. 3 is the development electrode 4 which, in the embodiment of FIG. modified by being directly grounded while the dye removing electrode 5 is connected to the bias voltage source 9 is connected to the development suppressing bias voltage in a similar manner as in Fig. to be biased. On the other hand, the magnet roller 2 is arranged so that its magnetic binding force is only sufficient Bristles of the magnetic brushes to form the dye particles T, and the developing electrode is arranged at such a position at which the magnetic binding force of the magnet roller 2 is weak, with the upper end of the electrode 4 from the surface of the outer cylinder 3 is held at a distance by the mounting plate 11. Since the rest of the structure and the Operations of the developing device D2 are the same as those of the developing device D1 of FIG a detailed description thereof can be dispensed with.

809839/0939

- 14 -

In Fig. 4 is another modification of the developing device of Fig. 2, where "at the modified developing device D3 differs from the embodiment of FIG. 2 in that the dye removing electrode which has been described in connection with the arrangement of FIG. 2 is omitted, the dye particles being used for the veils on the parts that have not become latent images only through the magnetic binding force of the magnetic roller can be removed, although the developing electrode 4 with the bias voltage source 3 for additional developing on similar Manner as in the embodiment of Fig. 2 is connected. It should be noted here that in the above case, the Magnetic roller 2 should be strong enough that it easily removes the dye particles that lead to the haze, so that such dye particles are removed at a point 6 on the outer cylinder 3, at which the surface of the outer Cylinder 3 of the photoreceptor surface 15 a is closest, i.e., at a point where the magnetic binding force of the magnet roller 2 is strongest. It should be noted that in the modified developing device D3 of Fig. 4 described above, the outer cylinder 3 is either can be electrically conductive or electrically insulating, since the removal of the dye particles T, which are responsible for the veil are responsible for the parts that have not become a picture, only caused by the magnetic binding force of the magnetic roller 2 will.

809839/0939

- 15 -

Pig. 5 shows a further modification of the developing device D1 of FIG. 2. In the modified developing device D4, the additional development and the removal of the dye particles which are responsible for the fog are only to be effected by adjusting the magnetic binding force. More specifically, the modified developing device D4 of Fig. 5 _{also dispenses with the dye removing electrode 5}} described in connection with Fig. 2 and the development electrode 4 'having a surface curved to meet the photoreceptor surface 15a is grounded and held at its upper edge in a position in which it is spaced from the surface of the outer cylinder 3 due to the fixing plate 11 and in which the magnetic binding force of the magnet roller 2 is weak, while the lower portion of the electrode 4 'gradually approaches the outer cylinder 3 so that it contacts the cylinder 3 at a position where the surface of the outer cylinder 3 is close to the photoreceptor surface 15a. It should be noted that in the modified developing device D4, the removal of the dye particles causing the fog is effected at the point 6 of the outer cylinder 3 where the strongest magnetic binding force occurs and where the surface of the outer cylinder 3 is the photoreceptor surface 15a is closest in a manner similar to the developing device D3 of FIG.

809839/0939

- 16 -

In Fig. 6, there is still another modification of the developing device D1 of FIG. 2 is shown. In the modified developing device D5, the dye removing electrode is 5 of the arrangement of FIG. 2 is replaced by a similar electrode 5 ', which is arranged opposite the development electrode 4 and is held in place by a mounting plate 12 where the photoreceptor surface 15a rests located at a greater distance from the surface of the outer cylinder 3, while a second development electrode 7 is provided at the point at which the dye removing electrode 5 is located in the arrangement of FIG. the Bias source 8 is connected to the developing electrode 4, and another bias source 10 is connected to the second Development electrode 7 connected to a development-enhancing bias voltage to the electrodes 4 and 7 for additional Develop while another bias source 9 'is connected to the dye removing electrode 5' is to apply a development suppressing bias voltage to it to remove the dye particles which lead to the veils. It should be noted here that in the "above arrangement, since the second developing electrode is at a position where the magnetic binding force is stronger than that of the developing electrode 4, the bias source 10 should have a higher potential than that of the development electrode 4, and that of the second development electrode 7 can be omitted if the additional development only by the development electrode 4 is sufficient

809839/0939

- 17 -

Dimensions can be achieved.

It should be noted that in the modifications of FIGS. 4 to 6, the description has been abbreviated since those Design features and functions of development facilities, which have not been specifically described therein, similar to the design features and function in the embodiment of Fig. 2 are.

It should also be noted that the additional development and removal of excess dye through the potential difference between the surface potential of the photoreceptor and the electrodes and also by the magnetic one Binding force is determined. In the extreme case, the bias for the additional developing can be the same polarity as that of the electrostatic latent image, or the bias to remove excess dye, the reverse Have polarity like that of the electrostatic latent image.

From the foregoing description, it can be seen that higher quality, high density copies with no fog on the not Parts that have become images without smearing or obscuring of the copied images are preserved during transmission, since the device according to the invention is designed so that the desired additional or excessive high density development is effected at least by the development electrode,

B09839 / 0939

- 18 -

while then the dye particles responsible for the
Veils are responsible for removing the dye
Electrode must be removed. Thus, development with the one-component developer can be effected advantageously by a dye powder image transfer type copier with an optimal result.

809839/0939

- 19 -

-Äf-

Blank page

Claims (7)

Patent claims j \ fj Magnetic brush developing device for an electrophotographic Copier__y_Q.m = dye powder image transfer type, which has a stationary cylinder which faces a photosensitive element moving in relation to it and which encloses a rotatable magnetic element, comprises a reservoir and means for dispensing magnetic dye particles onto the cylinder, characterized in that one in Arbeitsrichtüng Additional developing device arranged in front of the point of greatest approach between photosensitive element (15) and cylinder (3) (4, 4 ', 8) is provided which has a developing electrode (4, 4') arranged on the cylinder (3) / NSPECTED which points to the photosensitive element (15) and has approximately the same distance therefrom everywhere, and that a to remove excess dye particles (T) area determined by the photosensitive element (15) or a device (5, 9; 5 ', 9') is provided which or the between cylinder (3) and photosensitive element (15) in the working direction behind the additional developing device (4, 4 ') is arranged. 2. Device according to claim 1, characterized in that g e k e η η drawings-et, that the additional developing device (4, 4 ') is arranged at a point where the by the magnetic element (2) on the photosensitive element (15) exerted magnetic force is much smaller than at the point at which the cylinder (3) the photosensitive Element (15) closest to being the development electrode (4, 4 ·) is grounded. 3. Device according to claim 1, characterized in that the development electrode (4, 4 ') with a voltage source (8) for generating a bias voltage of opposite polarity to that of the latent image is. 4. Device according to one of claims 1 to 3, characterized in that the area (6) for removal 809839/0939 of dye particles (T) is provided at the point at which the surfaces of the cylinder (3) and the photosensitive element (15) are closest, the magnetic field strength being selected to be sufficiently large that its attraction to the dye particles (T) is greater than is the electrical attractive force of non-image forming parts of the photosensitive member (15). 5. Device according to one of claims 1 to 4, characterized in that an electrode (5, 5 ') removing dye particles is arranged on the cylinder (3) in the working direction behind the development electrode (4, 4') and is provided with a voltage source (9, 9 ¹ ) is connected to apply a bias voltage that has the same polarity as the electrostatic latent image. 6. Device according to one of claims 1 to 5, characterized in that the magnetic dye particles (T) have a sufficiently high electrical resistance that they transmit by ordinary corona transfer and that they are suitable for one-component development. 7. Device according to one of claims 1, 2, 4, 5 or 6, characterized in that the development electrode (4, 4 ¹ } is grounded and that in the area (6) or sodddd / 0939 281239S the means (5, 9; 5 ¹ , 9 ¹ ) for removing dye particles can remove at least the dye particles adhering to the parts of the electrostatic latent image which are not part of the image. ü. Device according to one of Claims 1, 3, 4, 5 or 6, characterized in that the developing electrode (4, 4 ') is connected to a voltage source (β) for generating a bias voltage which is opposite in polarity to that of the electrostatic latent image , and that in the area (6) or by the means (5, 9; 5 ', 9 ¹ ) for removing dye particles at least the dye particles can be removed which adhere to the parts of the electrostatic latent image which are not part of the image are. 80983970939